Method of controlling a continuous hot rolling mill

ABSTRACT

In a method of controlling a continuous hot rolling mill including a plurality of mill stands during acceleration thereof, variations in the screw down pressure (i.e., rolling load), in the speed of the material on the delivery side and in the thickness of the oil film of the back-up roll bearing of each mill stand at the time of acceleration, are anticipated, the width of the finished plates, types and compositions of the materials being rolled, plate gauges on the entrance side, pass speeds of the plates, the instants at which the accelerations are initiated, and accelerations are classified into a plurality of groups, an acceleration controlling schedule for each group that satisfies a relation that the product of the volume and speed of the material is constant is computed by an electronic computer associated with the rolling mill, and the roll gap and roll peripheral speed are controlled in accordance with the schedule for each mill stand so as to maintain the tension of the material between adjoining stands at a constant value.

United States Patent [1 1 Arimura et al.

11 3,733,866 1 May 22, 1973 Primary Examiner-Milton S. MehrAttorney-Flynn & Frishauf [57] ABSTRACT In a method of controlling acontinuous hot rolling mill including a plurality of mill stands duringacceleration thereof, variations in the screw down pressure (i.e.,rolling load), in the speed of the material on the delivery side and inthe thickness of the oil film of the back-up roll bearing of each millstand at the time of acceleration, are anticipated, the width of thefinished plates, types and compositions of the materials being rolled,plate gauges on the entrance side, pass speeds of the plates, theinstants at which the accelerations are initiated, and accelerations areclassified into a plurality of groups, an acceleration controllingschedule for each group that satisfies a relation that the product ofthe volume and speed of the material is constant is computed by anelectronic computer associated with the rolling mill, and the roll gapand roll peripheral speed are controlled in accordance with the schedulefor each mill stand so as to maintain the tension of the materialbetween adjoining stands at a constant value.

5 Claims, 5 Drawing Figures SIGNAL DISTRIBUTOR OF REVOLVING SPEED OFREDUCTION SCREW [54] METHOD OF CONTROLLING A CONTINUOUS HOT ROLLING MILL[75] Inventors: Tohru Arimura; Masaru Okado, both of Kawasaki; YujiFukuma; Yoshimitsu ldo, both of Fukuyama, all of Japan [73] Assignee:Nippon Kokan Kabushiki Kaisha,

Chiyoda-ku, Tokyo, Japan [22] Filed: June 9, 1971 [21] Appl.No.: 151,350

[30] Foreign Application Priority Data June 18, I970 Japan ..45/52579[52] US. Cl ..72/6 [51] Int. Cl. ..B2lb 37/00 [58] Field of Search..72/6-8, 72/16 [56] References Cited UNITED STATES PATENTS 3,507,1344/1970 Silva ..72/8 3,365,920 1/1968 Maekawa et al. 3,574,280 4/1971Smith, Jr. ..72/8

DIFFERENTIAL FUNETION GEN RATOR) (COMPUTER INPUT I DATA 1 TIMEACCELIERATION CONTROL APPARATUS Patented May 22. 1973 3,733,866

4 Sheets-Sheet 1 FIG] PRIOR ART FIG. 2

ACCELERATION PERIOD Patented May 22. 1973 3,733,866

4 Sheets-Sheet 3 TIME (SEC) FIG. 4

METHOD OF CONTROLLING A CONTINUOUS HOT ROLLING MILL BACKGROUND OF THEINVENTION This invention relates to a method of controlling a continuoushot rolling mill and more particularly to a method of controlling theacceleration of a continuous hot rolling mill wherein the roll gap andthe roll peripheral speed of each mill stand is controlled according toa predetermined pattern in order to maintain the gauge of the finishedplates at a constant value and to eliminate off-gauge products whenaccelerating the rolling mill.

Heretofore, in order to maintain the gauge of the finished plates at aconstant value, an automatic gauge control system (AGC) diagrammaticallyshown in FIG. 1 has generally been used. As shown, each mill stand of acontinuous rolling mill is provided with a reduction screw, S, anelectric motor, M, for driving the screw down, and a load cell, LC,responsive to the load or rolling pressure of the stand. According tothis system, the gauge of the finished plate that has passed through thefinal stand is measured by a suitable thickness measuring device, forexample an X-ray gauge meter, and when the gauge is brought into apredetermined range, the following method of control, termed as thelock-on operation, is performed manually or under control of anelectronic computer. More particularly, the plate gauge on the deliveryside of respective stands equipped with conventional BISRA type AGCsystems '(developed by British Iron and Steel Research Association)(normally, control of all intermediate stands excepting the first andlast stands) is computed according to an equation wherein h: plate gaugeon the delivery side of a stand P: screw down passage (i.e., rollingload) Po: screw down pressure or rolling load at the zero adjustment M:mill constant S: Set gap of the rolls Thereafter, due to theacceleration of the rolling speed, the temperature of the material andthe strain speed vary and the roll gap is varied in accordance with thevariation in the screw down pressure according to the followingequation, thus maintaining the plate gauge on the delivery side of thestand at a constant value Further, the deviation of the plate gaugemeasured by the X-ray gauge meter is fed back to the second andfollowing stands to supervise the plate gauge. As used herein, the termscrew down pressure is synonomous with rolling load.

However, an application of the prior controlling method to theacceleration of the rolling speed results in various troubles anddefects. For example, there is a trouble caused by the time lag in theraising or lowering of the screw. More particularly, as the accelerationof the material is increased, due to the variation in the temperatureand strain speed, the variation in the screw down pressure increases sothat it is necessary to rapidly raise or lower the screw after the AGCsystem has detected the variation in the screw down pressure. However,as there is a limit for the raising or lowering speed of the screw, thegauge of certain portions of the plate will deviate from a set value ifthe screw were raised or lowered after an instant at which the screwdown pressure varies. The length of such off gauge portions increasesproportionate to the acceleration and presents a substantial loss ofproduction. Further, there is the problem an incomplete compensation forthe variation in the thickness of the oil film. More particularly, thevariation in the roll peripheral speed and in the screw down pressureresults in the variation of the thickness of the oil film of thebearings for back-up rolls, thus varying the set value of the roll gap.Since, in the prior art control system, this variation is the set valueof the roll gap, it is controlled in terms of the variation in the screwdown pressure, control is effected in the opposite direction. In otherwords, while the plate gauge decreases with the roll gap, in response tothe increased screw down pressure, the prior art AGC system judges thatthe plate gauge is thick, and decreases the roll gap.

To eliminate this defect, an improvement has been proposed according towhich an acceleration compensation is made wherein the roll gap isvaried in response to the variation in the rolling speed. However,inasmuch as such an approach does not make an overall judgement by usingan electronic computer, it is impossible to eliminate the effects due tothe variation in the thickness of the oil film of the roll bearingscaused by the steel species being rolled, and thickness and width of thefinished plate. In the absence of the conventional AGC system, plategauge varies as shown in FIG. 2, thus producing inferior parts. FIG. 2shows the deviation of gauge in microns where a plate is rolled to havea gauge of 1.85 mm and a width of 800 mm at an acceleration of 0.496m/sec It is therefore an object of this invention to provide a novelmethod of controlling a continuous hot rolling mill capable ofmaintaining the plate gauge at a predetermined value when the mill isaccelerated.

Another object of this invention is to provide a new and improved methodof controlling a continuous hot rolling mill which can decreaseoff-gauge products by controlling the roll gap and roll peripheral speedaccording to a predetermined pattern determined by an electroniccomputer by anticipating various factors that vary as a result ofacceleration.

SUMMARY OF THE INVENTION According to this invention there is provided amethod of controlling a continuous hot rolling mill including aplurality of mill stands, comprising the steps of anticipatingvariations in the screw down pressure, in the speed of the material onthe delivery side and in the thickness of the oil film of the back-uproll bearing of each mill stand at the time of accelerating the rollingspeed, classifying the widths of the finished plates, types andcompositions of the steel being rolled, plate gauges on the entranceside, pass speeds of the plates, the instants at which the accelerationsare initiated, and accelerations into a plurality of groups, computingan acceleration controlling schedule for each group that satisfies arelation that the product of the volume and speed of the material isconstant on the delivery side by means of an electronic computerassociated with the rolling mill, and controlling the roll gap and theroll peripheral speed according to said schedule for each mill standwhereby to maintain the tension of the material between adjoining standsat a constant value.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a diagram to show a prior art AGC system;

FIG. 2 is a graph to show the variation in the plate gauge duringacceleration where the AGC system of the present invention is not used;

FIG. 3 is a diagram of a control system utilized to carry out the methodof this invention; and

FIG. 4 is a graph showing the transitional variation of roll gaps andFIG. 5 is a graph showing the transitional variation of the rollperipheral speed.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to this invention,various variables including widths of the finished plates, types andcompositions of the material, plate gauges on the entrance side, passspeeds of the plates, the instants at which the accelerations areinitiated, and accelerations are classitied into a plurality of groupsand various combinations of these groups are taken into consideration indetermining the acceleration control schedules.

The following computations are performed for each schedule. Moreparticularly, the plate gauge on the delivery side of each stand isdetermined by taking into consideration three variables viz. (a), thevariation with time in the screw down pressure caused by the variationsin the temperature and the strain speed (i.e., strain rate which occurduring acceleration (b), the variation with time in the speed of thematerial on the delivery side caused by the variation in the forwardslip due to the variation in the screw down pressure, and (c) thevariation with time in the thickness of the oil film of the back-up rollbearing caused by the variations in the peripheral speed of the roll andin the screw down pressure. Then, for a seven stand system, for example,shown in FIG. 1, patterns of variations with time of the roll gap androll peripheral speed that satisfy a relation that the product of thevolume and speed of the material is constant on the delivery side aredetermined for each roll stand by using following equations uU) M 410){1 +f41( i u( 1 +f (t))} wherein t: time,

S: set gap of the roll 11: plate gauge on the delivery side,

P: screw down pressure,

P0: zero adjust load,

M: mill constant,

6: sum of the thicknesses of the oil films on the side of the workingrolls of the upper and lower back-up rolls,

80: sum of the thicknesses of the oil films on the side of the workingrolls of the upper and lower back-up roll at the time of zeroadjustment,

V: peripheral speed of the roll,

f: forward slip i: stand number,

j: type of the acceleration control schedule, and

Stand d: the pivot stand.

These values of the variation with time in the roll gap S,,(t) and ofthe variation with time in the roll peripheral speed V,,(t) are storedin an on-line computer associated with a continuous hot rolling mill.

Reference is now made to FIG. 3. The following control is used for eachmaterial. Information regarding the finished width, type and compositionof the material, plate gauge on the delivery side, pass speed of theplate, the instant at which acceleration begins and acceleration arestored in the computer 1 as input data when the material passes throughthe last stand of a coarse mill. Then the acceleration control apparatus2 determines a particular acceleration control schedule for theparticular material based upon the command from the computer 1, and thedifferential function generator 3 receives an acceleration pattern foreach stand from the acceleration control apparatus 2, selects a group ofinput data and determines the time variation between roll gaps at eachstand, thereby giving commands for varying the roll gap and rollperipheral speed at each stand determined by the abovementionedacceleration control apparatus and differential function generatoraccording to their prescribed pattern concurrently with the initiationof the rolling operation of the material. In this manner, ananticipation control of roll gaps and roll peripheral speed is performedduring acceleration of the rolling operation.

EXAMPLE Variations with time in the roll gap and roll peripheral speedof the seventh stand under an acceleration control schedule for thefollowing material are shown respectively in FIGS. 4 and 5.

Width of the finished plate 1,000 mm Type of the steel Co 1 CompositionC 0.06, Mn 0.40

Plate thickness on the entrance side 30 mm Thickness of the finishedplate 1.2 mm

Pass Speed of the plate (F7) 11.7 m/sec.

Time at which acceleration begins 3 sec (The instant at which theleading edge of the material reaches a thermometer on the delivery sideof the finishing stand is taken as the origin of the time axis)Acceleration 0.888 m/sec Where the prior art method of control isapplied during acceleration of the mill in which the material isaccelerated after it has passed the finishing stand, the gauge ofcertain portion of the finished plate deviates from the prescribed valuewhereas according to this invention the roll gap and the roll peripheralspeed of each stand are varied in accordance with a predeterminedacceleration control schedule before the material reaches the finishingmill.

For this reason, it is possible to eliminate the production of off-gaugeportions due to the time lag in the raising and lowering of the screwwhich has been inevitable in the prior art method of control wherein, inorder to vary the roll gap and roll peripheral speed of each roll stand,the control is performed in response to the variation in the screw downpressure by anticipating the variation with time in the screw downpressure of each stand due to variations in the temperature and strainspeed of the material created at the time of the acceleration, thevariation with time in the speed of the material on the delivery sidecaused by the variation in the forward slip due to the variation in thescrew down pressure and the variation with time in the thickness of theoil film of the back-up roll bearing for the purpose of maintaining theproduct of the volume and speed of the material at a constant valve.

Further, since the variation with time of the thickness of the oil filmof the back-up roll bearing has been taken into consideration, theconventional AGC system 4 does not operate in the opposite direction.Thus the invention provides a perfect anticipation control wherein thevariation in the screw down pressure is also considered.

The invention is also applicable to a continuous cold rolling mill. Inthis case, by anticipating variations in the strain speed and in thethickness of the oil film of the back-up roll, the roll gap and the rollperipheral speed of each stand are varied according to a prescribedpattern for the purpose of preventing the gauge of the finished platedeviating from a predetermined value and preventing the tensions of thematerial between stands deviating from prescribed valves.

We claim:

1. A method of computerized control of a continuous rolling millincluding a plurality of mill stands, comprising the steps of:

storing information concerning the finished widths,

types and compositions of material which are to be operated on, plategauges on the entrance and delivery sides of the mill, pass speeds ofthe plates, the instants at which accelerations are initiated and theamounts of acceleration;

determining a particular acceleration control schedule of the millstands for the particular material being operated on in accordance witha given relationship which is a function of at least: said storedinformation, the variation with time in the screw down pressure causedby the variations in the temperature and the strain rate of the platewhich occur during acceleration, the variation with time in speed of thematerial on the delivery side caused by the variation in the forwardslip due to the variation in the screw down pressure, and the variationwith time in the thickness in the oil film of the back-up roll bearingcaused by the variations in the peripheral speed of the roll and in thescrew down pressure;

determining the time variation between change in roll gaps at eachsuccessive stand as a function of at least: said determined accelerationcontrol schedule, said stored information, the variation with time inthe screw down pressure caused by the variations in the temperature andthe strain rate of the plate which occur during acceleration, thevariation with time and speed of the material on the delivery sidecaused by the variation in the forward slip due to the variation in thescrew down pressure, and the variation with time in the thickness of theoil film of the back-up roll bearing caused by the variations in theperipheral speed of the roll and in the screw down pressure;

varying the roll gap at each stand as a function of said determined timevariation of roll gaps; and

controlling the roll peripheral speed at each stand as a roll peripheralspeed of said determined acceleration pattern;

to thereby provide anticipation control of roll gaps and roll peripheralspeed during acceleration of the rolling operation, such that therolling schedule satisfies the relation that the product of the volumeand speed of the material is constant on the delivery side of the mill.

2. The method according to claim 1 wherein said stored information isclassified into groups of information items, the groups having aparticular acceleration control schedule and roll gap change schedulethat satisfies said relation that the product of the volume and speed ofthe material is constant on the delivery side of the mill.

3. The method according to claim 2 wherein said determining stepsinclude determining into which groups of information items the operatingconditions and characteristics for a given strip fall.

4. The method according to claim 2 whereinselected combinations of saidgroups satisfy said relation.

5. A method according to claim 1 wherein said particular accelerationcontrol schedule and said time variation between change in roll gaps ateach successive stand are determined to satisfy said relation that theproduct of the volume and speed of the material is constant on thedelivery side by using the following equations:

ou) um) u( o a u 11( 0 ii u( r.l( 110) {1 frJ( u( (1 fij( (2 wherein t:time,

S: set gap of the roll,

h: plate gauge on the delivery side,

P: screw down pressure,

Po: zero adjust load,

M: mill constant,

8: sum of the thicknesses of the oil films on the side of the workingroll of the upper and lower back-up rolls,

: sum of the thicknesses of the oil films on the side of the workingrolls of the upper and lower back-up rolls at the time of zeroadjustment,

V: peripheral speed of the roll,

f: forward slip i: stand number,

j: type of the acceleration control schedule, and

Stand 4: the pivot stand.

1. A method of computerized control of a continuous rolling millincluding a plurality of mill stands, comprising the steps of: storinginformation concerning the finished widths, types and compositions ofmaterial which are to be operated on, plate gauges on the entrance anddelivery sides of the mill, pass speeds of the plates, the instants atwhich accelerations are initiated and the amounts of acceleration;determining a particular acceleration control schedule of the millstands for the particular material being operated on in accordance witha given relationship which is a function of at least: said storedinformation, the variation with time in the screw down pressure causedby the variations in the temperature and the strain rate of the platewhich occur during acceleration, the variation with time in speed of thematerial on the delivery side caused by the variation in the forwardslip due to the variation in the screw down pressure, and the variationwith time in the thickness in the oil film of the back-up roll bearingcaused by the variations in the peripheral speed of the roll and in thescrew down pressure; determining the time variation between change inroll gaps at each successive stand as a function of at least: saiddetermined acceleration control schedule, said stored information, thevariation with time in the screw down pressure caused by the variationsin the temperature and the strain rate of the plate which occur duringacceleration, the variation with time and speed of the material on thedelivery side caused by the variation in the forward slip due to thevariation in the screw down pressure, and the variation with time in thethickness of the oil film of the back-up roll bearing caused by thevariations in the peripheral speed of the roll and in the screw downpressure; varying the roll gap at each stand as a function of saiddetermined time variation of roll gaps; and controlling the rollperipheral speed at each stand as a function of said determinedacceleration pattern; to thereby provide anticipation control of rollgaps and roll peripheral speed during acceleration of the rollingoperation, such that the rolling schedule satisfies the relation thatthe product of the volume and speed of the material is constant on thedelivery side of the mill.
 2. The method according to claim 1 whereinsaid stored information is classified into groups of information items,the groups having a particular acceleration control schedule and rollgap change schedule that satisfies said relation that the product of thevolume and speed of the material is constant on the delivery side of themill.
 3. The method according to claim 2 wherein said determining stepsinclude determining into which groups of information items the operatingconditions and characteristics for a given strip fall.
 4. The methodaccording to claim 2 wherein selected combinations of said groupssatisfy said relation.
 5. A method according to claim 1 wherein saidparticular acceleration control schedule and said time variation betweenchange in roll gaps at each successive stand are determined to satisfysaid relation that the product of the volume and speed of the materialis constant on the delivery side by using the following equations:Sij(t) hij(t) -(Pij(t) - Po ij ) /Mij -( delta ij(t) - delta o ij ).................... (1) Vij(t) Hxj(t) . Vxj(t) . (1 + fxj(t) )/(hij(t). (1 + fij(t) ) .............. (2) wherein t: time, S: set gap of theroll, h: plate gauge on the delivery side, P: scRew down pressure, Po:zero adjust load, M: mill constant, delta : sum of the thicknesses ofthe oil films on the side of the working rolls of the upper and lowerback-up rolls, delta o: sum of the thicknesses of the oil films on theside of the working rolls of the upper and lower back-up rolls at thetime of zero adjustment, V: peripheral speed of the roll, f: forwardslip i: stand number, j: type of the acceleration control schedule, andx: denotes the ''''pivot'''' stand.